首页 | 本学科首页   官方微博 | 高级检索  
文章检索
  按 检索   检索词:      
出版年份:   被引次数:   他引次数: 提示:输入*表示无穷大
  收费全文   715004篇
  免费   8778篇
  国内免费   1949篇
电工技术   13122篇
综合类   704篇
化学工业   105127篇
金属工艺   30201篇
机械仪表   23202篇
建筑科学   17034篇
矿业工程   3807篇
能源动力   18503篇
轻工业   58949篇
水利工程   7616篇
石油天然气   12757篇
武器工业   43篇
无线电   80219篇
一般工业技术   141394篇
冶金工业   134643篇
原子能技术   14349篇
自动化技术   64061篇
  2021年   5952篇
  2020年   4310篇
  2019年   5545篇
  2018年   15009篇
  2017年   15260篇
  2016年   12947篇
  2015年   7107篇
  2014年   11283篇
  2013年   30439篇
  2012年   19575篇
  2011年   30304篇
  2010年   24886篇
  2009年   26676篇
  2008年   26914篇
  2007年   28027篇
  2006年   19300篇
  2005年   20080篇
  2004年   18328篇
  2003年   17893篇
  2002年   16212篇
  2001年   16004篇
  2000年   15097篇
  1999年   15899篇
  1998年   40668篇
  1997年   28632篇
  1996年   21974篇
  1995年   16349篇
  1994年   14388篇
  1993年   13974篇
  1992年   10205篇
  1991年   9640篇
  1990年   9372篇
  1989年   9145篇
  1988年   8569篇
  1987年   7586篇
  1986年   7335篇
  1985年   8291篇
  1984年   7766篇
  1983年   6963篇
  1982年   6437篇
  1981年   6621篇
  1980年   6210篇
  1979年   6185篇
  1978年   6009篇
  1977年   7104篇
  1976年   9483篇
  1975年   5167篇
  1974年   4869篇
  1973年   4948篇
  1972年   4060篇
排序方式: 共有10000条查询结果,搜索用时 0 毫秒
91.
For more than half a century, in nearly all western states, the regulatory agencies (the State Engineer or equivalent) used impairment of other water rights as the primary criterion for approving or rejecting change applications to move water to higher-valued uses. In recent years, however, protests to change applications have been brought by 'stakeholders' who do not own water rights, but who argue that they are affected by water transfers. Under the impairment rule, these parties do not have statutory standing to protest successfully. But they have brought legal suits to block transfers, and the courts have considered whether additional criteria involving 'impacts on social welfare' are needed to evaluate transfers. State Supreme Court rulings on such suits in Utah and Nevada are reviewed as prototype cases. The Utah court held that additional 'social welfare' criteria must be utilized by the State Engineer in evaluating change applications, whereas the Nevada court held that such criteria were already incorporated in existing water statutes and administrative practice. The critical question raised in the paper is whether existing state regulatory agencies can effectively implement a real 'social welfare' criterion to evaluate change applications. The conclusion is that they probably cannot, and that if they try, water allocations will be politicized to a much greater extent than they are now, and efficient market transfers will be impeded if not completely prevented.  相似文献   
92.
93.
伊朗卡尔黑多目标水利枢纽,首台机组于2002年9月投运。介绍了工程历史,并从导流系统遂洪道、渗漏控制和惟幕灌浆等方面介绍了工程的技术要求。  相似文献   
94.
A biochar from casein and its properties   总被引:2,自引:0,他引:2  
A biochar was prepared by pyrolysis of casein. A helium and mercury porosimeter were used to measure the true and apparent densities of the chars respectively, elemental and IR analysis were used to characterize the chemical composition of char. A SEM was used to observe the char surfaces in order to verify the presence of porosity. The biochar has 9.02% of nitrogen, content of porosity is 20%. The experimental results show that it is possible to prepare chars with relatively high porosity from casein for the further preparation of activated carbon.  相似文献   
95.
96.
In this paper, we describe a method for increasing the external efficiency of polymer light‐emitting diodes (LEDs) by coupling out waveguided light with Bragg gratings. We numerically model the waveguide modes in a typical LED structure and demonstrate how optimizing layer thicknesses and reducing waveguide absorption can enhance the grating outcoupling. The gratings were created by a soft‐lithography technique that minimizes changes to the conventional LED structure. Using one‐dimensional and two‐dimensional gratings, we were able to increase the forward‐directed emission by 47 % and 70 %, respectively, and the external quantum efficiency by 15 % and 25 %.  相似文献   
97.
Passivated single damascene copper SiO2 damascene lines were evaluated in combination with TiSiN and Ta(N)/Ta diffusion barriers. Leakage current, breakdown and time-dependent dielectric breakdown properties were investigated on a wafer level basis for temperatures ranging between room temperature and 150 °C. It is found that the leakage performance of the wafers with a TiSiN barrier is better at room temperature, but at 150 °C the performance levels out with Ta(N)/Ta. Time-dependent dielectric breakdown measurements at 150 °C show that the lifetime of the interconnect is higher with the selected Ta(N)/Ta barrier than for TiSiN.  相似文献   
98.
Efficient blue‐, green‐, and red‐light‐emitting organic diodes are fabricated using binuclear platinum complexes as phosphorescent dopants. The series of complexes used here have pyrazolate bridging ligands and the general formula CNPt(μ‐pz)2PtCN (where CN = 2‐(4′,6′‐difluorophenyl)pyridinato‐N,C2′, pz = pyrazole ( 1 ), 3‐methyl‐5‐tert‐butylpyrazole ( 2 ), and 3,5‐bis(tert‐butyl)pyrazole ( 3 )). The Pt–Pt distance in the complexes, which decreases in the order 1 > 2 > 3 , solely determines the electroluminescence color of the organic light‐emitting diodes (OLEDs). Blue OLEDs fabricated using 8 % 1 doped into a 3,5‐bis(N‐carbazolyl)benzene (mCP) host have a quantum efficiency of 4.3 % at 120 Cd m–2, a brightness of 3900 Cd m–2 at 12 V, and Commission Internationale de L'Eclairage (CIE) coordinates of (0.11, 0.24). Green and red OLEDs fabricated with 2 and 3 , respectively, also give high quantum efficiencies (~ 6.7 %), with CIE coordinates of (0.31, 0.63) and (0.59, 0.46), respectively. The current‐density–voltage characteristics of devices made using dopants 2 and 3 indicate that hole trapping is enhanced by short Pt–Pt distances (< 3.1 Å). Blue electrophosphorescence is achieved by taking advantage of the binuclear molecular geometry in order to suppress dopant intermolecular interactions. No evidence of low‐energy emission from aggregate states is observed in OLEDs made with 50 % 1 doped into mCP. OLEDs made using 100 % 1 as an emissive layer display red luminescence, which is believed to originate from distorted complexes with compressed Pt–Pt separations located in defect sites within the neat film. White OLEDs are fabricated using 1 and 3 in three different device architectures, either with one or two dopants in dual emissive layers or both dopants in a single emissive layer. All the white OLEDs have high quantum efficiency (~ 5 %) and brightness (~ 600 Cd m–2 at 10 V).  相似文献   
99.
Many organisations use decision models in their processes such as tables or trees to provide decision support to their operational divisions. For example, in fault management, customer contact centre operators usually use a decision model in the form of prescribed interviews. Based on the answers given by customers, the operator navigates through the decision model to reach an assessment of the problem. In order to achieve customer satisfaction and operational excellence, it is very important to constantly monitor the performance of a decision model not only on an overall level, but also on the level of individual decisions. In this paper we present a configurable business process analytics tool, known as the intelligent Universal Service Management System, that constantly monitors decision data and is capable of optimising the decisions based on high-level business objectives. We explain the various features of the software and show how it can be used to optimise decision processes. We also show how we can easily provide a customised version to monitor the performance of provision processes.  相似文献   
100.
Learning in multiple model adaptive control switch   总被引:1,自引:0,他引:1  
Including a learning mechanism in SMMAC (switched, multiple-model adaptive control) avoids the need for a priori knowledge of the model set of the plant to control and leads to a significant performance improvement with respect to the sole inclusion of an adaptive control channel in combination with switched fixed local controllers.  相似文献   
设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号